This invention relates to a process for preparing short chain alkyl aromatic compounds by alkylating an aromatic compound with a relatively short chain alkylating agent employing a synthetic porous crystalline material, or zeolite, as alkylation catalyst.
Zeolitic materials, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversion. Certain zeolitic materials are ordered, porous crystalline aluminosilicates having a definite crystalline structure as determined by X-ray diffraction, within which there are a large number of smaller cavities which may be interconnected by a number of still smaller channels or pores. These cavities and pores are uniform in size within a specific zeolitic material. Since the dimensions of these pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as "molecular sieves" and are utilized in a variety of ways to take advantage of these properties. Such molecular sieves, both natural and synthetic, include a wide variety of positive ion-containing crystalline silicates. These silicates can be described as a rigid three-dimensional framework of SiO.sub.4 and Periodic Table Group IIIA element oxide, e.g., AlO.sub.4, in which the tetrahedra are cross-linked by the sharing of oxygen atoms whereby the ratio of the total Group IIIA element, e.g., aluminum, and silicon atoms to oxygen atoms is 1:2. The electrovalence of the tetrahedra containing the Group IIIA element, e.g., aluminum, is balanced by the inclusion in the crystal of a cation, e.g., an alkali metal or an alkaline earth metal cation. This can be expressed wherein the ratio of the Group IIA element, e.g., aluminum, to the number of various cations, such as Ca/2, Sr/2, Na, K or Li, is equal to unity. One type of cation may be exchanged either entirely or partially with another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchange, it has been possible to vary the properties of a given silicate by suitable selection of the cation. The spaces between the tetrahedra are occupied by molecules of water prior to dehydration.
Prior art techniques have resulted in the formation of a great variety of synthetic zeolites. Many of these zeolites have come to be designated by letter or other convenient symbols, as illustrated by zeolite Z (U.S. Pat. No. 2,882,243); zeolite X (U.S. Pat. No. 2,882,244); zeolite Y (U.S. Pat. No. 3,130,007); zeolite ZK-5 (U.S. Pat. No. 3,247,195); zeolite ZK-4 (U.S. Pat. No. 3,314,752); zeolite ZSM-5 (U.S. Pat. No. 3,702,886); zeolite ZSM-11 (U.S. Pat. No. 3,709,979); zeolite ZSM-12 (U.S. Pat. No. 3,832,449); zeolite ZSM-20 (U.S. Pat. No. 3,972,983); zeolite ZSM-35 (U.S. Pat. No. 4,016,245); and zeolite ZSM-23 (U.S. Pat. No. 4,076,842), merely to name a few.
The SiO.sub.2 /Al.sub.2 O.sub.3 ratio of a given zeolite is often variable. For example, zeolite X can be synthesized with SiO.sub.2 /Al.sub.2 O.sub.3 ratios of from 2 to 3; zeolite Y, from 3 to about 6. In some zeolites, the upper limit of the SiO.sub.2 /Al.sub.2 O.sub.3 ratio is unbounded. ZSM-5 is one such example wherein the SiO.sub.2 /Al.sub.2 O.sub.3 ratio is at least 5 and up to the limits of present analytical measurement techniques. U.S. Pat. No. 3,941,871 (Re. 29,948) discloses a porous crystalline silicate made from a reaction mixture containing no deliberately added alumina in the recipe and exhibiting the X-ray diffraction pattern characteristic of ZSM-5. U.S. Pat. Nos. 4,061,724, 4,073,865 and 4,104,294 describe crystalline silicates of varying alumina and metal content.
Alkylation is one of the most important and useful reactions of hydrocarbons. Lewis and Bronsted acids, including a variety of natural and synthetic zeolites, have been used as catalysts. Alkylation of aromatic hydrocarbon compounds employing certain crystalline zeolite catalysts is known in the art. For instance, U.S. Pat. No. 3,251,897 describes liquid phase alkylation in the presence of crystalline aluminosilicates such as faujasite, heulandite, clinoptilolite, mordenite, dachiardite, zeolite X and zeolite Y. The temperature of such alkylation procedure does not exceed 600.degree. F., thereby maintaining patentee's preferable operating phase as substantially liquid.
Also, U.S. Pat. No. 2,904,607 shows alkylation of hydrocarbon compounds in the presence of certain crystalline zeolites. The zeolites described for use in this patent are crystalline metallic aluminosilicates, such as, for example, magnesium aluminosilicate.
U.S. Pat. Nos. 3,631,120 and 3,641,177 describe liquid phase processes for alxylation of aromatic hydrocarbons with olefins in the presence of certain zeolites. U.S. Pat. No. 3,631,120 discloses use of an ammonium exchanged, calcined zeolite having a silica to alumina mole ratio of between 4.0 and 4.9. U.S. Pat. No. 3,641,177 discloses use of a zeolite catalyst activated in a particular manner.
U.S. Pat. Nos. 3,751,504 and 3,751,506 describe the vapor phase alkylation of aromatic hydrocarbons with olefins in the presence of a specified type of zeolite catalyst.
U.S. Pat. Nos. 3,755,483 and 4,393,262 disclose the vapor phase reaction of propylene with benzene in the presence of zeolite ZSM-12, to product isopropylbenzene.
U.S. Pat. No. 4,469,908 discloses the alkylation of aromatic hydrocarbons with relatively short chain alkylating agents having from one to five carbon atoms employing ZSM-12 as alkylation catalyst.
Harper et al. have described a catalytic alkylation of benzene with propylene over a crystalline zeolite (Petrochemical Preprints, American Chemical Society, Vol. 22, No. 3, p. 1084, 1977). Extensive kinetic and catalyst aging studies were conducted with a rare earth exchanged Y-type zeolite (REY) catalyst.